Axial piston pumps are known to be used in hydraulically-actuated fuel injection systems. The efficient operation of such pumps is significant to the overall operation of the engine. Moreover, the ability of such pumps to operate free of maintenance is important to reduce downtime of the system. While efficient operation is an important design criteria, issues such as weight, size, cost, and ease of assembly influence the overall design of such pumps.
U.S. Pat. No. 6,035,828 to Anderson et al. describes a fixed displacement, variable delivery axial piston pump for a hydraulically-actuated fuel injection system. In the system, a high pressure common rail supplies hydraulic fluid to a plurality of hydraulically-actuated fuel injectors mounted in a diesel engine. The hydraulic fluid received in the common rail is pressurized by the fixed displacement axial piston pump that is driven directly by the engine. The pump includes a plurality pistons disposed in parallel about the central longitudinal axis of the pump, and reciprocation of the pistons is achieved by the rotation of an angled camming surface or swash plate that is biased against a proximal end of the pistons. Displacement of the pump is varied by a control valve that selectively varies the amount of pressurized fluid supplied to the pump outlet during the discharge stroke of each piston.
While the Anderson et al. pump performs well in operation, the axial forces created during a piston's discharge stroke act against the swash plate and the pump shaft connected to the pump shaft so as to require the use of axial bearings on the pump shaft. FIG. 2 of Anderson et al. illustrates two opposed tapered roller bearing arrangements for receiving axial forces created during pump operation. Such mechanical bearings have a limited life. Accordingly, the bearings or the entire pump need to be replaced each time the bearings fail. Further, the space, weight, cost and assembly aspects of the pump are adversely affected by the need to include such mechanical bearings.
The present invention provides an axial piston pump that avoids some or all of the aforesaid shortcomings in the prior art.